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salam every one, this is a topic from google web master centrale blog:
Webmaster level: Intermediate to Advanced Once in a while we get asked whether a site’s visibility in Google’s search results can be impacted in a negative way if it’s unavailable when Googlebot tries to crawl it. Sometimes downtime is unavoidable: a webmaster might decide to take a site down due to ongoing site maintenance, or legal or cultural requirements. Outages that are not clearly marked as such can negatively affect a site’s reputation. While we cannot guarantee any crawling, indexing or ranking, there are methods to deal with planned website downtime in a way that will generally not negatively affect your site’s visibility in the search results. For example, instead of returning an HTTP result code 404 (Not Found) or showing an error page with the status code 200 (OK) when a page is requested, it’s better to return a 503 HTTP result code (Service Unavailable) which tells search engine crawlers that the downtime is temporary. Moreover, it allows webmasters to provide visitors and bots with an estimated time when the site will be up and running again. If known, the length of the downtime in seconds or the estimated date and time when the downtime will be complete can be specified in an optional Retry-After header, which Googlebot may use to determine when to recrawl the URL. Returning a 503 HTTP result code can be a great solution for a number of other situations. We encounter a lot of problems with sites that return 200 (OK) result codes for server errors, downtime, bandwidth-overruns or for temporary placeholder pages (“Under Construction”). The 503 HTTP result code is the webmaster’s solution of choice for all these situations. As for planned server downtime like hardware maintenance, it’s a good idea to have a separate server available to actually return the 503 HTTP result code. It is important, however, to not treat 503 as a permanent solution: lasting 503s can eventually be seen as a sign that the server is now permanently unavailable and can result in us removing URLs from Google’s index. header('HTTP/1.1 503 Service Temporarily Unavailable'); header('Retry-After: Sat, 8 Oct 2011 18:27:00 GMT'); If you set up a 503 (Service Unavailable) response, the header information might look like this when using PHP. Similar to how you can make 404 pages more useful to users, it’s also a good idea to provide a customized 503 message explaining the situation to users and letting them know when the site will be available again. For further information regarding HTTP result codes, please see RFC 2616. this is a topic published in 2013... to get contents for your blog or your forum, just contact me at: devnasser@gmail.com
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Labels: advanced, crawling and indexing, intermediate
